Thanks for the replies.
After a day of changing wheels round, driving around... Again and again with different combinations. I seem to have sorted it.
Checking all the wheels... it seems that 2 wheels are not true. Ie buckled for want of a better phrase! The joys of cheap steel rims...
After over 7500km something tells me Chevy won't be so forth coming in replacing said wheels under warranty...
I will be getting the tie rod ends checked with the dealership as well.
Thanks Gearhead and Skids.